Catalytic converter assemblies currently used in the art for controlling emissions from industrial engines typically comprise a converter housing which is installed in the engine exhaust system and at least one catalytic element which is inserted into the converter housing. The catalytic element will typically comprise a wound strip of substrate material (preferably comprising alternating layers of flat and corrugated metal foil) which is impregnated (e.g., by chemisorption impregnation) with, or which otherwise carries, the converter reaction catalyst. The catalytic strip will commonly be wound in a circular pattern and will be held by a metal band which tightly surrounds the outer perimeter of the wound strip.
The wound catalytic converter elements heretofore used in the art have typically been formed by: (a) winding the catalytic element strip in a circular pattern to a desired diameter (typically at least 1.5 feet); (b) placing an appropriately sized, open metal holding band around the outer perimeter of the wound element strip; (c) pulling the holding band tight around the wound catalyst element using a ratchet strap or similar device such that the two ends of the open band meet; and then (d) welding the ends of the holding band together so that the band tightly encircles and holds the wound element strip.
In addition to catalytic converters, wound process elements are also commonly used in flame arrestors, air filters, heat exchangers, and other applications. In addition to metal substrates, examples of other types of substrate materials commonly used in such applications include, but are not limited to, plastics, paper filter media, and cloth filter media.
Wound substrates are typically used in catalytic converters and other applications in order to provide a high ratio of contact surface area to process gas flow. In extreme applications such as those encountered, for example, in the exhaust system of a continuous-duty reciprocating engine, the wound substrate must be of a strength, durability, and integrity to withstand continuous exposure to excessive temperatures and extreme pulsation and vibration, as well as significant variations and changes in the composition of the process gas.
Unfortunately, despite focused efforts in the industry on precision manufacturing, even the best wound substrate elements produced heretofore have been prone to looseness, sagging, and buckling of the element windings, and/or dimpling in the perimeter windings of the substrate—all of which degrade performance and reduce the useful life of the element.
Heretofore, it has not been possible to relieve minor inconsistencies in the shape, winding tension, and other features of a wound element until the “break-in” period where the new wound element is initially placed in actual operation and is exposed to the elevated temperature, vibration, and other harsh conditions of the operating environment. Depending on how the wound element is constrained, the relieved inconsistencies produced during break-in are sometimes distributed throughout the wound element, thus creating an overall looseness in the substrate. Loose substrate materials tend to vibrate excessively in the process flow, thus yielding fatigue failures and large holes or openings within the substrate over time. If, on the other hand, the relieved inconsistencies in the wound substrate are more concentrated, buckles, dimples, and/or gaps will be formed which will allow a significant amount of process gas to simply flow through the process element without contacting the wound substrate.
Predicting the eventual locations of dimples, buckles, gaps, and looseness in wound process elements has been extremely difficult, if not impossible. The imperfections which appear when relieved during the break-in period typically cause a rapid degradation of the element performance and can result in emissions exceedances, penalties for emissions violations, significant down time, and significantly higher costs for maintenance and operation.